Microcomputers generally operate in accordance with the sequence of instructions derived from a stored program. One important part of each instruction is the so-called "function" which is to be carried out by the processor in response to that instruction. As the processor must known how to respond to any particular "function" which arises in an instruction from the program, it is necessary to operate with a limited set of possible "functions". This is known as a "function set" and represents the range of functions which the processor is capable of identifying and obeying. Each time an instruction is received by the processor it has to translate the function of that instruction into one or more micro-instructions which control the transfer of electrical signals within the microcomputer so that signal exchanges occur between registers, memory and date paths in order to carry out the required instruction.
The development of integrated circuit technology has led to more components being provided on a microcomputer chip together with demand for an increased range of functions by the processor. This has caused function sets used in microcomputers to become more complex. The larger the function set, the more bit positions which are necessary in order to encode the required function. This in turn requires a larger processor and increase time delays in decoding the functions and carrying out the micro-instructions resulting from those functions.